1. Field of the Invention
The present invention relates to an X-ray angiography apparatus for generating a three-dimensional blood vessel image from images obtained before and after contrast medium injection.
2. Description of the Related Art
The blood vessels in the head run in a very complicated manner. In a case of an aneurysm, in particular, an operator often performs 3D-DSA (three-dimensional digital subtraction angiography) to determine an optimal observation angle which allows to check the neck of the aneurysm or comprehend the relationship between the neck and the dome or between the aneurysm and the parent vessel/capillary vessels near the aneurysm.
In 3D-DSA, the operator acquires a plurality of images in subtraction imaging directions before and after contrast medium injection by repeatedly performing acquisition while rotating an X-ray tube around the patient. In general, a two-dimensional projection image which is acquired before contrast medium injection such that the blood vessels are not contrasted is called a mask image, and a two-dimensional projection image which is acquired after contrast medium injection such that the blood vessels are contrasted is called a contrast image. Subtracting images before and after contrast medium injection upon aligning them in the same imaging directions makes it possible to mainly subtract a contrasted blood vessel portion. This method then generates a detailed three-dimensional blood vessel image by performing three-dimensional reconstruction processing for the extracted image of the blood vessel portion. This three-dimensional image is called a 3D-DSA image. 3D-DSA acquisition or rotational DSA, which is a basic technique thereof, is a technique of observing and reconstructing images upon subtracting images at the same angles. For this reason, mask images and contrast images are always acquired at the same angle sampling pitch.
There has been proposed a method of improving the visibility of a soft tissue by acquiring many projection images, e.g., 400 to 500 frames, and reconstructing a three-dimensional image from the many projection images using an X-ray angiography apparatus. In order to acquire projection images of 400 frames or more, it is necessary to rotate the arm slowly under the limitation of the acquisition rate on the X-ray detector side.
Rotating the arm slowly, however, will inevitably increase the amount of contrast medium used. At the time of diagnosis of disease in a blood vessel system, the operator performs imaging with a small number of projection images in clinical operation, inevitably resulting in a deterioration in the visibility of the soft tissue; refer to Jpn. Pat. Appln. KOKAI Publication No. 2004-171283.